The present invention is related to a handheld pipetting apparatus for metering liquids.
Handheld pipetting apparatuses or pipettes, respectively, are handleable metering apparatuses, which are used in the laboratory for metering liquids in particular.
Air cushion pipettes have a seat for detachably holding a pipette point. A displacement device for a gas is integrated into the pipette and communicatingly connected with the pipette point through a hole in the seat via a channel. An air cushion is displaced by means of the displacement device, so that liquid is aspirated through a point opening of the pipette point and ejected from it according to the direction of the displacement of the air cushion. Mostly, the displacement equipment is a cylinder with a plunger shiftable therein. The plunger is driven by means of a drive device.
Direct displacement pipettes co-operate with syringes, which have a syringe cylinder and a syringe plunger shiftable therein. The syringes can be coupled with the direct displacement pipettes and they are detachable from them. In this, the syringe cylinder is held on the direct displacement pipette and the syringe plunger is held on an accommodation body, which is shiftable by means of a drive device. By means of the drive device, the syringe plunger is moved to and from, so that liquid is aspirated through a hole of the syringe or ejected from the same, respectively.
Preferably, the pipette points or syringes, respectively, are made of plastic material and can be discarded after use or be replaced by a new pipette point or syringe (“single use article”).
Air cushion pipettes and direct displacement pipettes with manual and with electro-mechanical drive devices are known. In addition, there are air cushion pipettes and direct displacement pipettes with fixed volume and with adjustable volume. Further, there are single channel pipettes for the use with only one single pipette point or syringe, and multichannel pipettes for simultaneous use of a plurality thereof.
Advantages of air cushion pipettes with respect to direct displacement pipettes may be found in the greater metering accuracy at small amounts of liquid and when working with liquids having low vapour pressure or low viscosity, respectively. Further, in the smaller force required for actuation and the lower cost of the pipette points with respect to the syringes. However, in air cushion pipettes, liquid can come into the pipette through the channel and contaminate the same. Therefore, direct displacement pipettes are used in particular when contaminations of the pipette have to be avoided. Further, direct displacement pipettes have a smaller metering error than air cushion pipettes, when liquids having a high vapour pressure (ethanol or acetone, for instance) or having a higher viscosity (for instance glycol) have to be metered.
From DE 35 88 071 T2, the entire contents of which is incorporated herein by reference, an air cushion pipette is known, which can be equipped with different displacement devices, which each have a cylinder and a plunger arranged longitudinally shiftable therein. The displacement devices have a seat for a pipette point.
From DE 43 41 229 C2, the entire contents of which is incorporated herein by reference, and DE 10 2005 023 203 A1, the entire contents of which is incorporated herein by reference, direct displacement pipettes are known which can be equipped with different syringes.
DE 102 38 564 B4, the entire contents of which is incorporated herein by reference, discloses a pipette with a displacement device executed as a membrane pump, which is executed either as an air cushion pipette or as a direct displacement pipette.
Thus, the user reverts to air cushion pipettes or to direct displacement pipettes according to the metering task, which have to be kept at hand, cleaned, maintained and calibrated in the laboratory.
Proceeding from this, the present invention is based on the objective to facilitate the use of air cushion pipettes and of direct displacement pipettes for the user.